Water soluble, biocompatible compounds that impart lubricity to the surface of otherwise non-lubricious materials are desirable for use on medical devices which are inserted or implanted into the body. Such medical devices may include catheters that are utilized to deliver a stent, stent-graft, graft or vena cava filter, balloon catheters, other expandable medical devices and so forth. The industry has turned to hydrophilic lubricious coatings in order to overcome problems with commonly used hydrophobic coatings such as silicone, glycerin or olive oil.
Hydrophobic coatings have been known to bead up and run off when exposed to an aqueous environment, lose initial lubricity rapidly, and lack abrasion resistance. Residual amounts of silicone have also been known to cause tissue reaction and irritation in patients. The loss of lubricity can lead to discomfort during insertion into a patient, and damage to blood vessels and tissues due to frictional forces during insertion or removal of the device.
Hydrophilic coatings can be difficult to retain on the surface of a medical device when exposed to an aqueous environment such as that of bodily fluids. One particular class of hydrophilic coatings which has become popular for use are “hydrogels” which swell in an aqueous environment, and are capable of manifesting lubricity while in a “wet” or hydrated state. When hydrated, these substances have low frictional forces in humoral fluids including saliva, digestive fluids and blood, as well as in saline solution and water. Such substances include polyethylene oxides, optionally linked to the substrate surface by urethane or ureido linkages or interpolymerized with poly(meth)acrylate polymers or copolymers; copolymers of maleic anhydride; (meth)acryl amide polymers and copolymers; (meth)acrylic acid copolymers; polyurethanes; poly(vinyl pyrrolidone) and blends or interpolymers with polyurethanes; polysaccharides; and mixtures thereof.
Hydrogels alone, however, may still migrate from surfaces to which they are applied when exposed to an aqueous environment. One way in which to obtain improved surface retention has been through the use of polymeric networks in which one material is crosslinkable, or through the use of interpenetrating networks in which more than one material is crosslinkable.
The crosslinkable materials are typically cured through the addition of ultraviolet (UV) radiation. UV curable systems typically function by one of two mechanisms including a free radical mechanism or a cationic mechanism. One example of a class of materials which cure via a free radical mechanism are the acrylate functional crosslinkers. These acrylates are sensitive to oxygen in that they can form stable radicals in its presence, and thus require an inert gas purge.
Cationic cure mechanisms typically involve the use of a sulfonium or iodonium salt which decomposes when exposed to actinic UV radiation forming strong acids. This type of crosslinkable material is sensitive to the presence of a basic species and to humidity.
There remains a need in the art for an improved crosslinkable material useful in forming lubricious coatings which is not sensitive to the presence of oxygen or moisture.